The ADC field includes a variety of different types of ADC data carriers and ADC readers operable to read data encoded in such data carriers. For example, data may be encoded in machine-readable symbols, such as barcode symbols, area or matrix code symbols, and/or stack code symbols. Machine-readable symbols readers may employ a scanner and/or imager to capture the data encoded in the optical pattern of such machine-readable symbols. Other types of data carriers and associated readers exist, for example magnetic stripes, optical memory tags, and touch memories.
Other types of ADC carriers include RFID tags that may store data in a wirelessly accessible memory, and may include a discrete power source (i.e., an active RFID tag), or may rely on power derived from an interrogation signal (i.e., a passive RFID tag). RFID readers typically emit a radio frequency (RF) interrogation signal that causes the RFID tag to respond with a return RF signal encoding the data stored in the memory.
Identification of an RFID device or tag generally depends on RF energy produced by a reader or interrogator arriving at the RFID tag and returning to the reader. Multiple protocols exist for use with RFID tags. These protocols may specify, among other things, particular frequency ranges, frequency channels, modulation schemes, security schemes, and data formats.
Many ADC systems that use RFID tags employ an RFID reader in communication with one or more host computing systems that act as central depositories to store and/or process and/or share data collected by the RFID reader. In many applications, wireless communications is provided between the RFID reader and the host computing system. Wireless communications allow the RFID reader to be mobile, may lower the cost associated with installation of an ADC system, and permit flexibility in reorganizing a facility, for example a warehouse.
RFID tags typically include a semiconductor device (such as a chip) having the memory, circuitry, and one or more conductive traces that form an antenna. Typically, RFID tags act as transponders, providing information stored in the memory in response to the RF interrogation signal received at the antenna from the reader or other interrogator. Some RFID tags include security measures, such as passwords and/or encryption. Many RFID tags also permit information to be written or stored in the memory via an RF signal.
The read/write range and read/write quality of an RFID tag is often strongly dependent on the type of material composition of the object on which RFID tag is attached and/or on the type of material that is proximate to the RFID tag. As an illustration, a number of objects each with their own attached RFID tag may be present in or otherwise arranged in a pallet. When an RFID reader attempts to read these RFID tags, the RFID reader may successfully read some RFID tags, may read the data of some RFID tags incorrectly, and may not be able to read some RFID tags at all. For instance, the material composition and/or position of certain objects and/or parts of the pallet may block the interrogation signal being sent from the RFID reader, thereby preventing the interrogation signal from reaching some of the RFID tags. Further, the material composition and/or position of certain objects and/or parts of the pallet may block or distort or otherwise interfere with the quality of the return signal sent by RFID tags that did successfully receive the interrogation signal, thereby resulting in erroneous information received by the RFID reader.
Other problems can arise when two or more of such pallets are positioned proximate to each other. Thus, when a user attempts to use the RFID reader to read the RFID tags located in a first pallet, the RFID reader may inadvertently also read the RFID tags located in a second pallet positioned near the first pallet. This result may be undesirable, for example, if the user is intending to accurately read the RFID tags in only the first pallet.
The above-discussed problems can be compounded if, for example, the RFID reader has poor focusing capability and/or if the user of the RFID reader is not particularly skilled in properly aiming the RFID reader to read target RFID tags. Accordingly, return signals from RFID tags that are not of interest may be received, the RFID tags of interest may not properly receive the interrogation signal, etc.